NPT thread chart (ASME B1.20.1)
American National Standard Taper Pipe threads have a taper of 1 in 16 on diameter (1.7899°). Threads per inch depend only on pipe size.
| NPT size | Threads per inch | Pitch (mm) | Pipe OD (mm) | Pipe OD (in) |
|---|---|---|---|---|
| 1/8" | 27 | 0.941 | 10.3 | 0.406 |
| 1/4" | 18 | 1.411 | 13.7 | 0.539 |
| 3/8" | 18 | 1.411 | 17.1 | 0.673 |
| 1/2" | 14 | 1.814 | 21.3 | 0.839 |
| 3/4" | 14 | 1.814 | 26.7 | 1.051 |
| 1" | 11.5 | 2.209 | 33.4 | 1.315 |
| 1-1/4" | 11.5 | 2.209 | 42.2 | 1.661 |
| 1-1/2" | 11.5 | 2.209 | 48.3 | 1.902 |
| 2" | 11.5 | 2.209 | 60.3 | 2.374 |
| 2-1/2" | 8 | 3.175 | 73.0 | 2.874 |
| 3" | 8 | 3.175 | 88.9 | 3.500 |
| 3-1/2" | 8 | 3.175 | 101.6 | 4.000 |
| 4" | 8 | 3.175 | 114.3 | 4.500 |
| 5" | 8 | 3.175 | 141.3 | 5.563 |
| 6" | 8 | 3.175 | 168.3 | 6.626 |
| 8" | 8 | 3.175 | 219.1 | 8.626 |
| 10" | 8 | 3.175 | 273.1 | 10.752 |
| 12" | 8 | 3.175 | 323.9 | 12.752 |
Frequently asked questions
How many threads per inch is 1/2 inch NPT?
14 threads per inch.
What is the difference between NPT and BSPT?
NPT has a 60° thread angle; BSPT (ISO 7) has 55° and different pitches for some sizes, so they are not interchangeable.
What is the taper of NPT threads?
1 in 16 on diameter, or 3/4 inch per foot.
Last updated 2026-11-02